Coating liquid for electrophotographic photoreceptor, electrophotographic photoreceptor, and image forming method and apparatus using the photoreceptor

ABSTRACT

A photoreceptor including an electroconductive substrate; an undercoat layer located overlying the electroconductive substrate and including titanium oxide which has an average particle diameter greater than 0.05 μm and less than 0.20 μm and which includes rutile titanium oxide in an amount of from 10 to 100% by weight based on total weight of the titanium oxide; and a photosensitive layer located overlying the undercoat layer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a coating liquid for anelectrophotographic photoreceptor, an electrophotographic photoreceptorwhich is prepared using the coating liquid, and electrophotographicimage forming method and apparatus using the electrophotographicphotoreceptor. In addition, the present invention also relates to anelectrophotographic process cartridge using the electrophotographicphotoreceptor.

[0003] 2. Discussion of the Background

[0004] Conventionally, inorganic photosensitive materials such as Se,CdS and ZnO have been used for electrophotographic photoreceptors. Inaddition, organic photosensitive materials have been developed and usedfor electrophotographic photoreceptors because of having advantages ofhigh photosensitivity and heat stability and less toxicity over theinorganic photosensitive materials. Therefore, at the present timephotoreceptors using an organic photosensitive material are typicallyused for current copiers and printers.

[0005] In electrophotographic image forming apparatus such as printers,copiers and facsimiles, a series of image forming processes such ascharging, light irradiating, developing and transferring processes istypically performed. Such image forming apparatus at least includes acharger, an imagewise light irradiator, an image developer(particularly, a reverse image developer), a transfer device and aphotoreceptor. The image forming apparatus having such a constitutiontend to produce abnormal images after long repeated use.

[0006] Recently, digitization rapidly progresses and is applied to imageforming apparatus such as printers and copiers. Therefore,photoreceptors which are sensitive to laser light (i.e., monochromaticlight) emitted by a laser diode, are needed to be used for such digitalimage forming apparatus. Not to produce abnormal images such as moiré isone of the requisites of the photoreceptors, and an undercoat layerformed between an electroconductive substrate and a photosensitive layerplays a important role in preventing the moiré problem. For example, atechnique in which a particulate metal oxide or a particulate organicmaterial is included in an undercoat layer is proposed to prevent themoiré problem.

[0007] The following techniques have been proposed with respect to theundercoat layer.

[0008] (1) Japanese Laid-Open Patent Publication No. (hereinafterreferred to as JOP) 11-15181 discloses a photoreceptor which includes analuminum or aluminum alloy substrate having a surface which is subjectedto an anodizing treatment, followed by a mechanical polishing treatmentand a sealing treatment using hot water or a sealing treatment whilehumidifying, and a photosensitive layer located on the substrate;

[0009] (2) JOP 10-301314 discloses a photoreceptor which has anelectroconductive substrate, and an undercoat layer and a photosensitivelayer, which are overlaid on the substrate, wherein a composition inwhich a kind of organoalkoxy siloxane is mixed with a colloidal aluminaand which is crosslinked upon application of heat thereto is used as theundercoat layer;

[0010] (3) JOP 10-90931 discloses a photoreceptor which has anelectroconductive substrate, and an undercoat layer and a photosensitivelayer, which are overlaid on the substrate, wherein the undercoat layerincludes a resin and titanium oxide subjected to a heat treatment;

[0011] (4) JOP 5-204181 discloses a photoreceptor which has a substrate,and an electroconductive polyaniline layer and a photosensitive layer,which are overlaid on the substrate; and

[0012] (5) JOP 8-44096 discloses a photoreceptor which has a substrate,and an undercoat layer and a photosensitive layer, which are overlaid onthe substrate, wherein the undercoat layer includes a heat-crosslinkedresin at a volume content ratio of from 0.5 to 0.6 and titanium oxidehaving an average particle diamter not greater than 0.4 μm;

[0013] (6) JOP 9-34152 discloses a photoreceptor which has anelectroconductive substrate, and an undercoat layer and a photosensitivelayer, which are overlaid on the substrate, wherein the substrate ismade of aluminum, an Al—Mn alloy, an Al—Mg alloy or an Al—Mg—Si alloy,and the undercoat layer includes a compound selected from the groupconsisting of metal alkoxides, organic metal chelate compounds, silanecoupling agents and reaction products thereof;

[0014] (7) JOP 9-292730 discloses a photoreceptor for reversedevelopment in which a photosensitive layer is formed on an anodizedsurface of an electroconductive substrate made of aluminum or analuminum alloy, wherein the anodized surface has a profile in which aninterval Sm between a projected portion and an adjacent projectedportion is from 0.3 to 250 μm; the maximum height Rt of the projectedportions is from 0.5 to 2.5 μm; and the gloss of the anodized surface isnot less than 60 gloss; and

[0015] (8) JOP 10-83093 discloses a photoreceptor in which an undercoatlayer is formed between an electroconductive substrate and aphotosensitive layer, wherein the undercoat layer includes a particulatetitanium oxide having a surface including at least zirconium oxide.

[0016] In the above-mentioned photoreceptors (1) to (8), variousconstitutions and/or materials are applied to the undercoat layer or ananodic oxide layer is applied as the undercoat layer to preventinjection of holes into a photosensitive layer (or a charge generationlayer), resulting in prevention of occurrence of black spot images.However, the above-mentioned photoreceptors are not satisfactory becauserecently photoreceptors do not meet the current requirements therefor,such as producing high quality images and having high durability.

[0017] As mentioned above, photoreceptors are needed not to producemoiré which is caused by light interference. In order to avoid the moiréproblem, photoreceptors including a metal oxide such as titanium oxidein their undercoat layer are typically used.

[0018] An undercoat layer including titanium oxide is typically formedby coating a coating liquid, in which titanium oxide is dispersed in aresin and a dispersion medium, on an electroconductive substrate. Sincemetal oxides such as titanium oxide have a specific gravity much greaterthan a resin and a dispersion medium used in the coating liquid, thedispersion stability and coating properties of the resultant coatingliquids are typically poor. Therefore a uniform undercoat layer cannotbe formed because metal oxides included in the coating liquids tend toeasily aggregate. Therefore, aggregated particles tend to be included inthe resultant undercoat layers. Alternatively there is a problem in thatthe productivity of the coating liquids is low because such coatingliquids as including an aggregated metal oxide are typically disposedof.

[0019] Because of these reasons, a need exists for anelectrophotographic photoreceptor which can produce high quality imagesfor a long period of time without producing abnormal images such asblack spots.

SUMMARY OF THE INVENTION

[0020] provide an undercoat layer coating liquid which can form anundercoat layer without producing coating defects such as pinholes.

[0021] Another object of the present invention is to provide aphotoreceptor which can produce high quality images for a long period oftime without producing abnormal images such as black spots.

[0022] Yet another object of the present invention is to provide animage forming method, an image forming apparatus and a processcartridge, by which high quality images can be produced for a longperiod of time without producing abnormal images such as black spots.

[0023] Briefly these objects and other objects of the present inventionas hereinafter will become more readily apparent can be attained by acoating liquid including at least a binder resin, titanium oxide and anorganic solvent, wherein the titanium oxide includes rutile titaniumoxide in an amount of from 10 to 100% by weight based on total weight ofthe titanium oxide, and wherein the titanium oxide is dispersed in thecoating liquid and has an average particle diameter (R) greater than0.05 μm and less than 0.20 μm, and.

[0024] The purity of the titanium oxide is preferably not less than99.0%.

[0025] The content of rutile titanium oxide is preferably from 10 to 70%and more preferably from 30 to 70%.

[0026] In another aspect of the present invention, anelectrophotographic photoreceptor is provided which includes anelectroconductive substrate, an undercoat layer located overlying thesubstrate and a photosensitive layer located overlying the undercoatlayer, wherein the undercoat layer includes a binder resin and titaniumoxide, and wherein the titanium oxide included in the undercoat layerhas an average particle diameter (R) greater than 0.05 μm and less than0.20 μm, and includes rutile titanium oxide in an amount of from 10 to100% by weight based on total weight of the titanium oxide.

[0027] The purity of the titanium oxide is preferably not less than99.0%.

[0028] The content of rutile titanium oxide is preferably from 10 to 70%and more preferably from 30 to 70%.

[0029] The photosensitive layer preferably includes a charge generationlayer and a charge transport layer, which are overlaid.

[0030] In yet another aspect of the present invention, an image formingmethod is provided which includes the steps of charging thephotoreceptor of the present invention mentioned above; irradiating thephotoreceptor with imagewise light to form an electrostatic latent imageon the photoreceptor; developing the electrostatic latent image with adeveloper to form a toner image on the photoreceptor; and transferringthe toner image on a receiving material, wherein the irradiating step isperformed using light emitted a laser diode or light emitting diode, andwherein the developing step is performed using a reverse developingmethod.

[0031] In a further aspect of the present invention, an image

[0032] In a further aspect of the present invention, an image formingapparatus is provided which includes at least a charger, a lightirradiator, an image developer, an image transfer device, a dischargerand the photoreceptor of the present invention.

[0033] In a still further aspect of the present invention, a processcartridge is provided which includes at least the photoreceptor of thepresent invention and at least one of a charger, a light irradiator, animage developer, an image transfer device and a discharger.

[0034] These and other objects, features and advantages of the presentinvention will become apparent upon consideration of the followingdescription of the preferred embodiments of the present invention takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Various other objects, features and attendant advantages of thepresent invention will be better understood from the detaileddescription when considered in connection with the accompanying drawingsin which like reference characters designate like corresponding partsthroughout and wherein:

[0036]FIG. 1 is a schematic view illustrating the cross section of anembodiment of the photoreceptor of the present invention;

[0037]FIG. 2 is a schematic view illustrating the cross section of anembodiment of the photoreceptor of the present invention, which has alayered photosensitive layer;

[0038]FIG. 3 is a schematic view illustrating the cross section ofanother embodiment of the photoreceptor of the present invention, whichhas a layered photosensitive layer and a protective layer;

[0039]FIG. 4 is a schematic view illustrating the main part of anembodiment of the image forming apparatus of the present invention; and

[0040]FIG. 5 is a schematic view illustrating the main part of anembodiment of the process cartridge of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0041] At first, titanium oxide for use in the coating liquid of thepresent invention will be explained in detail.

[0042] The titanium oxide for use in the coating liquid of the presentinvention, which has an average particle diameter (R) greater than 0.05μm and less than 0.20 μm are typically prepared by a method usingchlorine. Namely, a titan slag which is a raw material of titanium oxideis chlorinated to prepare titanium tetrachloride. Then the thus preparedproduct is subjected to a separation treatment, a condensation treatmentand a purification treatment, and then oxidized to prepare raw titaniumoxide.

[0043] The thus prepared raw titanium oxide is pulverized and classifiedto prepare titanium oxide for use in the present invention. The rawtitanium oxide is optionally subjected to a surface treatment. In thiscase, the surface-treated titanium oxide is filtered and the cake iswashed and then dried. The dried surface-treated titanium oxide powderis pulverized to prepare titanium oxide which has a treated surface andwhich is for use in the coating liquid of the present invention.

[0044] In order to prepare such titanium oxide as having a desiredaverage particle diameter R (i.e., 0.05 μm<R<0.20 μm), the primaryparticle diameter of the raw titanium oxide should be controlled whenthe titanium tetrachloride is oxidized.

[0045] By using the thus prepared titanium oxide in an undercoat layercoating liquid, the resulting coating film (i.e., the undercoat layer)has good hiding power, i.e., an undercoat layer can be formed on thesurface of an electroconductive substrate without forming pinholes inthe undercoat layer. In addition, the precipitation speed of thetitanium oxide in the undercoat layer coating liquid is very slow, andthereby the undercoat layer coating liquid does not cause aprecipitation problem. Namely, the undercoat layer coating liquid of thepresent invention has good preservation properties.

[0046] When the titanium oxide used in the undercoat layer has aparticle diameter smaller than 0.05 μm, the titanium oxide tends to havea high activity at the surface thereof, and thereby the electrostaticproperties of the resultant photoreceptor deteriorate.

[0047] When the titanium oxide used in the undercoat layer has aparticle diameter greater than 0.20 μm, the titanium oxide in thecoating liquid tends to easily precipitate, i.e., the stability of thecoating liquid deteriorates. In addition, pinholes tend to be formed inthe resultant undercoat layer. In the present invention, the particlediameter distribution of titanium oxide is measured with respect to adispersion in which the titanium oxide is strongly dispersed in water.

[0048] In the present invention, the purity of titanium oxide mainlydepends on the factors such as the purity of the raw material, themanufacturing method used, whether or not the titanium oxide issubjected to a surface treatment, and the degree of the surfacetreatment (i.e., the quantity of the surface treatment agent adhered tothe titanium oxide). When the method using chlorine is used, high-puritytitanium oxide can be prepared.

[0049] Titanium oxide for use in the coating liquid of the presentinvention preferably has a purity not less than 99.0%. Hygroscopicmaterials such as Na₂O and K₂O, and ionic materials are typicallyincluded in titanium oxide as impurities. When the purity of thetitanium oxide used in the undercoat layer is less than 99.0%, theelectrostatic properties of the resultant photoreceptor tend to largelyvary particularly when the photoreceptor is used under high humidityconditions and/or repeatedly used for a long period of time. Suchimpurities cause image defects such as black spots.

[0050] In the present invention, the purity of titanium oxide isdetermined based on JIS K5116.

[0051] In addition, the titanium oxide for use in the undercoat layerpreferably includes rutile-form titanium oxide in an amount of from 10to 100% by weight based on total weight of the titanium oxide. Ingeneral, titanium oxide has a crystal as specific gravity, refractiveindex and hardness thereof are different. The crystal form, anatase orrutile, of titanium oxide depends on the sintering conditions when thetitanium oxide is prepared. When sintered under a mild condition, theresultant titanium oxide tends to have an anatase form, and as thesintering temperature is increased, the crystal form is changed to arutile form. Therefore, by controlling the sintering conditions, thetitanium oxide for use in the present invention, i.e., titanium oxideincluding rutile form titanium oxide at a desired content (i.e., from 10to 100%, preferably from 10 to 70%, and more preferably from 30 to 70%),can be prepared.

[0052] The reason why the titanium oxide including rutile form titaniumoxide at a proper content are preferable in the present invention is notyet determined, but by using such titanium oxide, occurrence of imagedefects such as background development (background fouling) can beavoided.

[0053] In the present invention, the content of rutile titanium oxide intitanium oxide can be determined by an X-ray diffraction method.Specifically, the content of rutile titanium oxide (hereinafter referredto as the rutile titanium oxide content) can be determined by comparingthe intensity of a peak of the X-ray diffraction spectrum specific torutile titanium oxide with the intensity of another peak specific toanatase titanium oxide.

[0054] The method for measuring the rutile titanium oxide content is asfollows:

[0055] content is as follows:

[0056] 1. Each of mixtures of hundred-percent rutile titanium oxide withhundred-percent anatase titanium oxide which are fully mixed atpredetermined ratios is subject to an X-ray diffraction analysis toprepare a working curve illustrating a relationship between rutiletitanium oxide contents and X-ray peak ratios (Ratio); and

[0057] 2. a titanium oxide sample is subjected to the X-ray diffractionanalysis to determine the rutile titanium oxide content of the sampleusing the working curve.

[0058] The Ratio is determined as follows:

[0059] (1) in the X-ray diffraction spectrum, the net integral strength(NET(R)) of a peak specific to anatase titanium located at an angle offrom 24.80° to 25.80° and the net integral strength (NET(A)) of a peakspecific to rutile titanium located at an angle of from 26.70° to 28.20°are determined; and

[0060] (2) the Ratio is determined by the following equation:

Ratio=NET(R)/{NET(R)+NET(A)}.

[0061] Then the photoreceptor of the present invention will be explainedin detail referring to drawings.

[0062]FIG. 1 is a schematic view illustrating the cross section of anembodiment of the photoreceptor of the present invention.

[0063] The photoreceptor includes an electroconductive substrate 11, anundercoat layer 13 which is located on the electroconductive substrate11 and which includes titanium oxide, and a photosensitive layer 15located on the undercoat layer 13.

[0064]FIG. 2 is a schematic view illustrating the cross section ofanother embodiment of the photoreceptor of the present invention.

[0065] The photoreceptor includes an electroconductive substrate 11, anundercoat layer 13 which is located on the electroconductive substrate11 and which includes titanium oxide, and a charge generation layer 17and a charge transport layer 19 are overlaid on the undercoat layer 13.

[0066]FIG. 3 is a schematic view illustrating the cross section of yetanother embodiment of the photoreceptor of the present invention.

[0067] As illustrated in FIG. 3, a protective layer 21 can be formed onthe charge transport layer 19 of the photoreceptor illustrated in FIG.2.

[0068] Suitable materials for use as the electroconductive substrate 11include materials having a volume resistance not greater than 10¹⁰Ω·cm.Specific examples of such materials include plastic cylinders, plasticfilms or paper sheets, on the surface of which a metal such as aluminum,nickel, chromium, nichrome, copper, gold, silver, platinum and the like,or a metal oxide such as tin oxides, indium oxides and the like, isdeposited or sputtered. In addition, as the substrate 11, a sheet ofnickel, stainless steel or the like metal, and a tube which is preparedby tubing a metal such as aluminum, nickel, stainless steel or the likemetal using a method such as impact ironing or direct ironing, followedby a surface treatment such as cutting, super finishing, polishing andthe like can also be used. In addition, tubes which are made of analuminum alloy such as JIS3003 type aluminum alloys, JIS5000 typealuminum alloys, JIS6000 type aluminum alloys and the like aluminumalloys and which are formed by a method such as extrude ironing (EI)methods, extrude drawing (ED) methods, direct ironing (DI) methods andimpact ironing (II) methods, optionally followed by a surface cuttingtreatment using a diamond cutting tool, a surface polishing treatmentand/or an anodizing treatment, can also be used.

[0069] Further, endless belts of a metal such as nickel, stainless steeland the like metal, which have been disclosed, for example, in JapaneseLaid-Open Patent Publication No. 52-36016, can also be used as thesubstrate 11.

[0070] Furthermore, substrates, in which a coating liquid including abinder resin and an electroconductive powder is coated on the supportsmentioned above, can be used as the substrate 11. Specific examples ofthe electroconductive powder include carbon black, acetylene black,powders of metals such as aluminum, nickel, iron, nichrome, copper,zinc, silver and the like, and metal oxides such as electroconductivetin oxides, ITO and the like. Specific examples of the binder resininclude known thermoplastic resins, thermosetting resins andphoto-crosslinking resins, such as polystyrene, styrene-acrylonitrilecopolymers, styrene-butadiene copolymers, styrene-maleic anhydridecopolymers, polyesters, polyvinyl chloride, vinyl chloride-vinyl acetatecopolymers, polyvinyl acetate, polyvinylidene chloride, polyarylates,phenoxy resins, polycarbonates, cellulose acetate resins, ethylcellulose resins, polyvinyl butyral resins, polyvinyl formal resins,polyvinyl toluene, poly-N-vinyl carbazole, acrylic resins, siliconeresins, epoxy resins, melamine resins, urethane resins, phenolic resins,alkyd resins and the like.

[0071] Such an electroconductive layer can be formed by coating acoating liquid in which an electroconductive powder and a binder resinare dispersed or dissolved in a proper solvent such as tetrahydrofuran,dichloromethane, methyl ethyl ketone, toluene and the like, and thendrying the coated liquid.

[0072] In addition, substrates, in which an electroconductive resin filmis formed on a surface of a cylindrical substrate using aheat-shrinkable resin tube which is made of a combination of a resinsuch as polyvinyl chloride, polypropylene, polyesters, polyvinylidenechloride, polyethylene, chlorinated rubber and fluorine-containingresins, with one or more of the electroconductive materials mentionedabove, can also used as the substrate 11.

[0073] The undercoat layer 13 includes titanium oxide and a resin asmain components. Since the photosensitive layer (e.g., thephotosensitive layer 15 in FIG. 1 or the charge generation layer 17 inFIGS. 2 and 3) is typically formed on the undercoat layer by coating aliquid including an organic solvent, the resin included in the undercoatlayer preferably has good resistance to general organic solvents.

[0074] Specific examples of such resins include water-soluble resinssuch as polyvinyl alcohol resins, casein and polyacrylic acid sodiumsalts; alcohol soluble resins such as nylon copolymers andmethoxymethylated nylon resins; and thermosetting resins capable offorming a three-dimensional network such as polyurethane resins,melamine resins, phenolic resins, alkyd-melamine resins, epoxy resinsand the like resins.

[0075] The weight ratio (T/R) of the titanium oxide (T) to the resin (R)in the undercoat layer is preferably from 3/1 to 8/1. When the weightratio is too small, the carrier transportability of the undercoat layerdeteriorates, resulting in increase of the residual potential of theresultant photoreceptor and deterioration of the photo-response thereof.In contrast, when the weight ratio is too large, the undercoat layer hasmany air spaces, and thereby air bubbles are formed when aphotosensitive layer coating liquid is coated on the undercoat layer,resulting in formation of coating defects in the photosensitive layer.

[0076] Similarly to the photosensitive layer mentioned below, theundercoat layer 13 can be formed by coating a coating liquid including aresin, titanium oxide and a proper solvent using a proper coatingmethod.

[0077] The thickness of the undercoat layer 13 is preferably from 1.0 to10 μm.

[0078] Then the photosensitive layer will be explained.

[0079] The charge generation layer 17 includes a charge generationmaterial, and a binder resin as necessary.

[0080] Specific examples of the binder resin include polyamide,polyurethane, epoxy resins, polyketone, polycarbonate, silicone resins,acrylic resins, polyvinyl butyral, polyvinyl formal, polyvinyl ketone,polystyrene, polysulfone, poly-N-vinylcarbazole, polyacrylamide,polyvinyl benzal, polyester, phenoxy resins, vinyl chloride-vinylacetate copolymers, polyvinyl acetate, polyphenylene oxide, polyamides,polyvinyl pyridine, cellulose resins, casein, polyvinyl alcohol,polyvinyl pyrrolidone, and the like resins.

[0081] The addition amount of the binder resin is from 0 to 500 parts byweight, and preferably from 10 to 300 parts by weight, per 100 parts byweight of the charge generation material included in the chargegeneration layer.

[0082] Specific examples of the charge generation materials includephthalocyanine pigments such as metal phthalocyanine and metal-freephthalocyanine, azulenium pigments, squaric acid methine pigments,perylene pigments, anthraquinone pigments, polycyclic quinone pigments,quinoneimine pigments, diphenyl methane pigments, triphenyl methanepigments, benzoquinone pigments, naphthoquinone pigments, cyaninepigments, azomethine pigments, indigoid pigments, bisbenzimidazolepigments, and azo pigments such as monoazo pigments, bisazo pigments,asymmetric bisazo pigments, trisazo pigments and tetraazo pigments.

[0083] Specific examples of the azo pigments include azo pigments havinga carbazole skeleton (disclosed in JOP 53-95033), azo pigments having atriphenylamine skeleton (disclosed in JOP 53-132547), azo pigmentshaving a stilbene skeleton (disclosed in JOP 53-138229), azo pigmentshaving a dibenzothiophene skeleton (disclosed in JOP 54-21728), azopigments having a fluorenone skeleton (disclosed in JOP 54-22834), azopigments having an oxadiazole skeleton (disclosed in JOP 54-12742), azopigments having a bisstilbene skeleton (disclosed in JOP 54-17733), azopigments having a distyryloxadiazole skeleton (disclosed in JOP54-2129), azo pigments having a distyrylcarbazole skeleton (disclosed inJOP 54-17734), and the like pigments.

[0084] The charge generation layer 17 is prepared by, for example, thefollowing steps:

[0085] (1) preparing a coating liquid by mixing one or more chargegeneration materials mentioned above with a solvent such as isopropanol,aceton, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane,dioxolan, ethyl cellosolve, ethyl acetate, methyl acetate,dichloromethane, dichloroethane, monochlorobenzene, cyclohexane, xylene,ligroin and the like, optionally together with a binder resin and anadditive, and then dispersing the materials with a ball mill, anattritor, a sand mill, an ultrasonic dispersing machine or the likedispersing machine;

[0086] (2) coating on a substrate the coating liquid, which may bediluted as necessary, using a dip coating method, a spray coatingmethod, a bead coating method, a nozzle coating method, a spinnercoating method, a ring coating method or the like method; and

[0087] (3) drying the coated liquid to form a charge generation layer.

[0088] The thickness of the charge generation layer 17 is preferablyfrom about 0.01 to about 5 μm, and more preferably from about 0.1 toabout 2 μm.

[0089] Then the charge transport layer 19 will be explained.

[0090] The charge transport layer 19 includes a charge transportmaterial as a main component.

[0091] The charge transport layer 19 can be formed, for example, by thefollowing method:

[0092] (1) a charge transport material and a binder resin are dispersedor dissolved in a proper solvent such as tetrahydrofuran, dioxane,dioxolan, anisole, toluene, monochlorobenzene, dichloroethane, methylenechloride, cyclohexanone or the like solvent, to prepare a chargetransport layer coating liquid; and

[0093] (2) coating the charge transport layer coating liquid on thecharge generation layer and drying the coated liquid, to form a chargetransport layer.

[0094] Charge transport materials are classified into positive-holetransport materials and electron transport materials.

[0095] Specific examples of the electron transport materials includeelectron accepting materials such as chloranil, bromanil,tetracyanoethylene, tetracyanoquinodimethane,2,4,7-trinitro-9-fluorenon, 2,4,5,7-tetanitroxanthone,2,4,8-trinitrothioxanthone,2,6,8-trinitro-4H-indeno[1,2-b]thiophene-4-one,1,3,7-trinitrodibenzothiphene-5,5-dioxide,3,5-dimethyl-3′,5′-di-tert-butyl-4,4′-diphenoquinone and the likematerials. These electron transport materials can be used alone or incombination.

[0096] Specific examples of the positive-hole transport materialsinclude known materials such as poly-N-vinylcarbazole and itsderivatives, poly-γ-carbazolylethylglutamate and its derivatives,pyrene-formaldehyde condensation products and their derivatives,polyvinyl pyrene, polyvinyl phenanthrene, polysilane, oxazolederivatives, oxadiazole derivatives, imidazole derivatives,monoarylamines derivatives, diarylamines derivatives, triarylaminesderivatives, stilbene derivatives, α-phenyl stilbene derivatives,benzidine derivatives, diarylmethane derivatives, triarylmethanederivatives, 9-styrylanthracene derivatives, pyrazoline derivatives,divinyl benzene derivatives, hydrazone derivatives, indene derivatives,butadiene derivatives, pyrene derivatives, bisstilbene derivatives,enamine derivatives, thiazole derivatives, triazole derivatives,phenazine derivatives, acridine derivatives, benzofuran derivatives,benzimidazole derivatives, thiophene derivatives and the like materials.

[0097] These positive hole transport materials can be used alone or incombination.

[0098] Specific examples of the binder resin for use in the chargetransport layer include known thermoplastic resins, thermosetting resinsand photo-crosslinking resins, such as polystyrene,styrene-acrylonitrile copolymers, styrene-butadiene copolymers,styrene-maleic anhydride copolymers, polyesters, polyvinyl chloride,vinyl chloride-vinyl acetate copolymers, polyvinyl acetate,polyvinylidene chloride, polyarylates, phenoxy resins, polycarbonates(e.g., bisphenol A-form polycarbonates and bisphenol Z-formpolycarbonates), cellulose acetate resins, ethyl cellulose resins,polyvinyl butyral resins, polyvinyl formal resins, polyvinyl toluene,poly-N-vinyl carbazole, acrylic resins, silicone resins, epoxy resins,melamine resins, urethane resins, phenolic resins, alkyd resins, andpolycarbonate copolymers disclosed in JOPs 5-158250 and 6-51544.

[0099] In addition, charge transport polymers, which have both a binderfunction and a charge transport function, can also be used as the binderresin in the charge transport layer 19.

[0100] Specific examples of such charge transport polymers include thefollowing.

[0101] (a) polymers having a carbazole ring in their main chain and/or aside chain, such as poly-N-vinylcarbazole, and polymers disclosed inJOPs 50-82056, 54-9632, 54-11737, and 4-183719;

[0102] (b) polymers having a hydrazone unit in their main chain and/or aside chain, such as polymers disclosed in JOPs 57-78402, and 3-50555;

[0103] (c) polysilylene polymers such as polymers disclosed in JOPs63-285552, 5-19497 and 5-70595; and

[0104] (d) polymers having a tertiary amine unit in their main chainand/or a side chain, such as N,N-bis(4-methylphenyl)-4-aminopolystyrene, and polymers disclosed in JOPs 1-13061, 1-19049, 1-1728,1-105260, 2-167335, 5-66598, and 5-40350.

[0105] The addition amount of the binder resin is preferably from 0 to150 parts by weight per 100 parts by weight of the charge transportmaterial included in the charge transport layer.

[0106] The charge transport layer optionally includes one or moreadditives such as plasticizers, leveling agents and antioxidants.

[0107] Specific examples of the plasticizers include halogenatedparaffins, dimethyl naphthalene, dibutyl phthalate, dioctyl phthalate,tricresyl phosphate, and polymers and copolymers such as polyesters.

[0108] Specific examples of the leveling agents include silicone oilssuch as dimethyl silicone oils and methylphenyl silicone oils, andpolymers and oligomers having a perfluoralkyl group in their side chain.The addition amount of the leveling agents is from 0 to 1 part by weightper 100 parts by weight of the binder resin included in the chargetransport layer.

[0109] Specific examples of the antioxidants include hindered phenolcompounds, sulfur-containing compounds, phosphorus-containing compounds,hindered amines, pyridine derivatives, piperidine derivatives,morpholine derivatives, and the like materials. The addition amount ofthe antioxidant is preferably from 0 to 5 parts by weight per 100 partsby weight of the binder resin included in the charge transport layer.

[0110] The thickness of the charge transport layer 19 is preferably from5 to 50 μm.

[0111] Next, the single-layered photosensitive layer 15 will beexplained.

[0112] The single-layered photosensitive layer 15 includes a chargegeneration material, a charge transport material and a binder resin asmain components. The photosensitive layer can be formed by coating acoating liquid in which a charge generation material, a charge transportmaterial and a binder resin are dissolved or dispersed in a propersolvent such as tetrahydrofuran, cyclohexanone, dioxane, dichloroethaneand butanone, using a dispersion machine such as ball mills, attritorsand sand mills, and then drying the coated liquid. Specific examples ofthe coating method include dipping methods, spray coating methods, rollcoating methods, blade coating methods and the like coating methods.

[0113] Suitable binder resins for use in the single-layeredphotosensitive layer include the resins mentioned above for use in thecharge transport layer. The resins mentioned above for use in the chargegeneration layer can also be used in combination with the resinsmentioned above for use in the charge transport layer.

[0114] In addition, a photosensitive layer including a combination of aneutectic complex including a pyrylium dye and a bisphenol A-formpolycarbonate resin with a charge transport material can also be used asthe single-layered photosensitive layer. This layer can also be formedby a method similar to the method mentioned above.

[0115] The single-layered photosensitive layer may also include one ormore additives such as plasticizers, leveling agents and antioxidants.Specific examples thereof are mentioned above.

[0116] The thickness of the single-layered photosensitive layer ispreferably from 5 or 50 μm.

[0117] In the photoreceptor of the present invention, the protectivelayer 21 is formed overlying the photosensitive layer (e.g., thephotosensitive layer 15 and charge transport layer 19) as an outermostlayer to improve the durability of the photoreceptor.

[0118] The protective layer includes a resin as a main component.

[0119] Specific examples of the resins for use in the protective layer21 include ABS resins, ACS resins, olefin-vinyl monomer copolymers,chlorinated polyethers, aryl resins, phenolic resins, polyacetal,polyamides, polyamideimide, polyacrylates, polyarylsulfone,polybutylene, polybutylene terephthalate, polycarbonate,polyethersulfone, polyethylene, polyethylene terephthalate, polyimides,acrylic resins, polymethylpentene, polypropylene, polyphenyleneoxide,polysulfone, polystyrene, AS resins, butadiene-styrene copolymers,polyurethane, polyvinyl chloride, polyvinylidene chloride, epoxy resins,polyesters and the like resins.

[0120] The protective layer preferably includes a filler such as organicfillers and inorganic fillers to improve the abrasion resistance of thephotoreceptor.

[0121] Specific examples of the organic fillers include powders offluorine-containing resins such as polytetrafluoroethylene, siliconeresin powders and the like powders. Specific examples of the inorganicfillers include titanium oxide, aluminum oxide, tin oxide, zinc oxide,zirconium oxide, magnesium oxide, silica and the like inorganicmaterials. The inorganic fillers may be subjected to a surfacetreatment.

[0122] In addition, the protective layer may include a charge transportmaterial.

[0123] The protective layer can be formed by the method as mentionedabove for use in the charge transport layer and photosensitive layer.The thickness of the protective layer is preferably from 0.1 to 10 μm.

[0124] In addition, a layer of amorphous carbon or amorphous siliconcarbide which is formed by a vacuum thin film forming method can also beused as the protective layer 21.

[0125] The photoreceptor of the present invention may include anintermediate layer between the photosensitive layer (e.g., thephotosensitive layer 15 or charge transport layer 19) and the protectivelayer 21. The intermediate layer includes a resin as a main component.Specific examples of the resin include polyamides, alcohol-soluble nylonresins, water-soluble butyral resins, polyvinyl butyrals, polyvinylalcohols, and the like resins.

[0126] The intermediate layer is also formed by the method mentionedabove for use in the charge transport layer, photosensitive layer andprotective layer.

[0127] The thickness of the intermediate layer is preferably from 0.05to 2 μm.

[0128] The electrophotographic image forming apparatus and processcartridge of the present invention will be explained referring todrawings.

[0129]FIG. 4 is a schematic view illustrating an embodiment of the imageforming apparatus of the present invention.

[0130] In FIG. 4, numeral 41 denotes a photoreceptor. The photoreceptor41 is the photoreceptor of the present invention which includes at leastan electroconductive substrate, an undercoat layer which is formedoverlying the substrate by coating the coating liquid of the presentinvention, and a photosensitive layer located overlying the undercoatlayer.

[0131] Around the photoreceptor 41, a discharging lamp 42 configured toirradiate the photoreceptor with light to reduce the residual potentialof the photoreceptor 41, a charger 43 configured to charge thephotoreceptor 1, an eraser 44 configured to erase a charged area whichis unnecessary, an imagewise light irradiator 45 configured to irradiatethe photoreceptor 41 with imagewise light to form an electrostaticlatent image on the photoreceptor 41, an image developer 46 configuredto develop the latent image with a developer including a toner to form atoner image on the photoreceptor 41, a cleaning unit including acleaning brush 54 and a cleaning blade 55 configured to clean thesurface of the photoreceptor 41 are arranged while contacting or beingset closely to the photoreceptor 41.

[0132] The toner image formed on the photoreceptor 41 is transferred ona receiving paper 49 fed by a pair of registration rollers 48 at atransfer device (i.e., a pair of a transfer charger 50 and a separatingcharger 51). The receiving paper 49 having the toner image thereon isseparated from the photoreceptor 41 by a separating pick 52.

[0133] In the image forming apparatus of the present invention, apre-transfer charger 47 and a pre-cleaning charger 53 may be arranged ifdesired.

[0134] Although the photoreceptor 41 has a cylindrical shape in FIG. 4,sheet photoreceptors or endless belt photoreceptors can also be used.

[0135] As the charger 43, the pre-transfer charger 47, the transfercharger 50, the separating charger 51 and the pre-cleaning charger 53,all known chargers such as corotrons, scorotrons, solid state chargers,roller chargers and brush chargers can be used.

[0136] As the transfer device, the above-mentioned chargers can be used.

[0137] In FIG. 4, a toner image formed on the photoreceptor 41 isdirectly transferred onto the receiving paper 49. However, the tonerimage on the photoreceptor 41 may be transferred onto an intermediatetransfer medium and then secondly transferred onto a receiving paper.

[0138] Suitable light sources for use in the imagewise light irradiator45 and the discharging lamp 42 include fluorescent lamps, tungstenlamps, halogen lamps, mercury lamps, sodium lamps, light emitting diodes(LEDs), laser diodes (LDs), light sources using electroluminescence(EL), and the like. In addition, in order to obtain light having adesired wave length range, filters such as sharp-cut filters, band passfilters, near-infrared cutting filters, dichroic filters, interferencefilters, color temperature converting filters and the like can be used.

[0139] The above-mentioned lamps can be used for not only the processesmentioned above and illustrated in FIG. 4, but also other processesusing light irradiation, such as a transfer process including lightirradiation, a discharging process, a cleaning process including lightirradiation and a pre-exposure process.

[0140] When the toner image formed on the photoreceptor 41 by the imagedeveloper 46 is transferred onto the receiving paper 49, all of thetoner image are not transferred on the receiving paper 49, and residualtoner particles remain on the surface of the photoreceptor 41. Theresidual toner is removed from the photoreceptor 41 by the fur brush 54or the cleaning blade 55. The residual toner remaining on thephotoreceptor 41 can be removed by only a cleaning brush. Suitablecleaning brushes include known cleaning brushes such as fur brushes andmag-fur brushes. However, when the image developer has a cleaningfunction, it is not necessary to provide the cleaning brush 54 and thecleaning blade 55.

[0141] When the photoreceptor 41 which is previously charged positively(or negatively) is exposed to imagewise light, an electrostatic latentimage having a positive (or negative) charge is formed on thephotoreceptor 41. When a latent image having a positive (or negative)charge is developed with a toner having a negative (or positive) charge,a positive image can be obtained. In contrast, when a latent imagehaving a positive (or negative) charge is developed with a toner havinga positive (or negative) charge, a negative image (i.e., a reversalimage) can be obtained.

[0142] As the image developer 46, known developing devices can be used.

[0143] The image forming apparatus illustrated in FIG. 4 is only oneexample of the image forming apparatus of the invention, and the imageforming apparatus of the invention is not limited thereto.

[0144] For example, an image forming unit may be set in copiers,facsimile machines and printers, as a process cartridge. The processcartridge means an image forming unit (or device) which includes atleast a photoreceptor, and at least one of a charger, an imagewise lightirradiator, an image developer, an image transfer device, a cleaner, anda discharger.

[0145] Various process cartridges can be used in the present invention.An embodiment of the process cartridge of the present invention isillustrated in FIG. 5. In FIG. 5, numeral 101 denotes the photoreceptorof the present invention. Similarly to the image forming apparatus asillustrated in FIG. 4, a charger 102 configured to charge thephotoreceptor 101; an imagewise light irradiator 103 configured toirradiate the photoreceptor 101 with imagewise light to form anelectrostatic latent image on the photoreceptor 101; an image developer104 configured to develop the electrostatic latent image with adeveloper including a toner to form a toner image on the photoreceptor101; an image transfer device 106 configured to transfer the toner imageon a receiving material 105 such as paper; a cleaner 107 configured toremove the residual toner on the photoreceptor 101; and a discharge lamp108 configured to remove the residual potential remaining on thephotoreceptor 101, are arranged around the photoreceptor 101. Numeral109 denotes a fixer configured to fix the toner image, resulting information of a hard copy.

[0146] The receiving material 105, image transfer device 106, dischargelamp 108 and fixer 109 are not included in this process cartridge. Asthe light irradiation processes, imagewise light irradiation,pre-cleaning light irradiation, and discharging light irradiation areillustrated in FIG. 5, but other known light irradiation processes suchas pre-transfer light irradiation, preliminary light irradiation priorto the imagewise light irradiation can also be performed on thephotoreceptor 101.

[0147] Having generally described this invention, further understandingcan be obtained by reference to certain specific examples which areprovided herein for the purpose of illustration only and are notintended to be limiting. In the descriptions in the following examples,the numbers represent weight ratios in parts, unless otherwisespecified.

EXAMPLES Example 1

[0148] Formation of Undercoat Layer

[0149] The following components were mixed and dispersed for 72 hoursusing a ball mill to prepare an undercoat layer coating liquid (U-1₀).Titanium oxide 70 (purity of 99.5 %, rutile titanium oxide content of40%, and average particle diameter of 0.07 μm) Alkyd resin 18 (BEKKOLITEM6401-50-S from Dainippon Ink & Chemicals Inc., solid content of 50%)Melamine resin 10 (SUPER BEKKAMINE L121-60 from Dainippon Ink &Chemicals Inc., solid content of 60%) Methyl ethyl ketone 100 

[0150] The undercoat layer coating liquid was coated on an aluminum drumwhich was prepared by cutting and which has a diameter of 30 mm and alength of 340 mm. The coated liquid was dried at 130° C. for 20 minutesto prepare an undercoat layer having a thickness of 3.5 μm.

[0151] In addition, the undercoat layer coating liquid was preserved for3 months and 6 months under normal temperature condition (23±2° C.)while agitated, to prepare undercoat coating liquids U-1₃ and U-1₆. Thecoating liquids were also coated on such an aluminum drum as preparedabove.

[0152] Formation of Charge Generation Layer

[0153] The following components were mixed and dispersed for 72 hoursusing a ball mill.

[0154] (4 parts of a polyvinyl butyral (BM-1 from Sekisui Chemical Co.,Ltd.) were dissolved in 150 parts of cyclohexanone)

[0155] Then 210 parts of cyclohexanone were added to the dispersion andthe mixture was further dispersed for 3 hours using the ball mill.

[0156] The charge generation layer coating liquid was coated on theabove-prepared three undercoat layers and the coated liquids were driedat 130° C. for 10 minutes to prepare a charge generation layer having athickness of 0.2 μm on each undercoat layer.

[0157] Formation of Charge Transport Layer

[0158] The following components were mixed to prepare a charge transportlayer coating liquid.

[0159] Charge transport material having the following

[0160] The charge transport layer coating liquid was coated on eachcharge generation layer and the coated liquid was dried at 135° C. for20 minutes to form a charge transport layer having an average thicknessof 25 μm.

[0161] Thus, three photoreceptors (i.e., P-1₀, P-1₃ and P-1₆ of Example1 were prepared.

[0162] The thus prepared undercoat layer coating liquid andphotoreceptor in Example 1 were evaluated as follows.

[0163] 1. Evaluation of the Undercoat Layer Coating Liquids

[0164] (1) Dispersion Stability

[0165] The dispersion stability of the coating liquid U-1₀ was evaluatedas follows.

[0166] (a) the coating liquid is contained in a test tube having aheight of 10 cm;

[0167] (b) the test tube is capped and allowed to settle for 1 month;

[0168] (c) the height (H) of the clear portion (i.e., the supernatantliquid portion) of the coating liquid is measured.

[0169] Namely, the shorter the height of the clear portion, the betterthe dispersibility of the coating liquid. The height of the clearportion of the undercoat layer coating liquid U-1₀ was 7 mm.

[0170] (2) Coating Property

[0171] The coated undercoat layer was visually observed to determine thenumber of large particles (i.e., aggregates of titanium oxide) having adiameter not less than 0.5 mm in the undercoat layer. Undercoat layerswere formed by coating the initial undercoat layer coating liquid, andundercoat layer coating liquids which had been preserved for 3 monthsand 6 months while agitating (i.e., coating liquids U-1₀, U-1₃ andU-1₆). As a result, there was no large particle in the three undercoatlayers.

[0172] 2. Evaluation of Photoreceptors

[0173] (1) Black Spots

[0174] Each of the photoreceptors P-1₀, P-1₃ and P-1₆ was set in acopier IMAGIO MF220 manufactured by Ricoh Co., Ltd., and 20,000 imageswere continuously produced. The 20,000^(th) image (a white image of A4size) was visually observed to determine the number of black spotshaving a diameter not less than 0.5 mm.

[0175] As a result, there was no black spot in the images produced bythe photoreceptors P-1₀, P-1₃ and P-1₆.

[0176] (2) Surface Potentials

[0177] The surface potentials (VL and VD) of a lighted area (L) and adark area (D) of each photoreceptor were measured at the beginning andend of the 20,000-sheet running test. The voltage applied to the charger(i.e., charging roller) was −1680V.

Example 2

[0178] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.5%, a rutile titanium oxide content of 40%, and anaverage particle diameter of 0.15 μm.

[0179] Thus, undercoat layer coating liquids U-2₀, U-2₃ and U-2₆ andphotoreceptors P-2₀, P-2₃ and P-2₆ were prepared.

Example 3

[0180] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.97%, a rutile titanium oxide content of 10% and anaverage particle diameter of 0.07 μm.

[0181] Thus, undercoat layer coating liquids U-3₀, U-3₃ and U-3₆ andphotoreceptors P-3₀, P-3₃ and P-3₆ were prepared.

Example 4

[0182] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.97%, a rutile titanium oxide content of 40% and anaverage particle diameter of 0.07 μm.

[0183] Thus, undercoat layer coating liquids U-4₀, U-4₃ and U-4₆ andphotoreceptors P-4₀, P-4₃ and P-4₆ were prepared.

Example 5

[0184] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.97%, a rutile titanium oxide content of 60% and anaverage particle diameter of 0.07 μm.

[0185] Thus, undercoat layer coating liquids U-5₀, U-5₃ and U-5₆ andphotoreceptors P-5₀, P-5₃ and P-5₆ were prepared.

Example 6

[0186] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.97%, a rutile titanium oxide content of 100% andan average particle diameter of 0.07 μm.

[0187] Thus, undercoat layer coating liquids U-6₀, U-6₃, and U-6₆ andphotoreceptors P-6₀, P-6₃ and P-6₆ were prepared.

Example 7

[0188] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 98.0%, a rutile titanium oxide content of 40% and anaverage particle diameter of 0.15 μm.

[0189] Thus, undercoat layer coating liquids U-7₀, U-7₃ and U-7₆ andphotoreceptors P-7₀, P-7₃ and P-7₆ were prepared.

Example 8

[0190] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.97%, a rutile titanium oxide content of 70% and anaverage particle diameter of 0.07 μm.

[0191] Thus, undercoat layer coating liquids U-8₀, U-8₃ and U-8₆ andphotoreceptors P-8₀, P-8₃ and P-8₆ were prepared.

Comparative Example 1

[0192] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.5%, a rutile titanium oxide content of 40% and anaverage particle diameter of 0.02 μm.

[0193] Thus, undercoat layer coating liquids H-1₀, H-1₃ and H-1₆ andphotoreceptors HP-1₀, HP-1₃ and HP-1₆ were prepared.

Comparative Example 2

[0194] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.5%, a rutile titanium oxide content of 40% and anaverage particle diameter of 0.30 μm.

[0195] Thus, undercoat layer coating liquids H-2₀, H-2₃ and H-2₆ andphotoreceptors HP-2₀, HP-2₃ and HP-2₆ were prepared.

Comparative Example 3

[0196] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 98.0%, a rutile titanium oxide content of 40% and anaverage particle diameter of 0.35 μm.

[0197] Thus, undercoat layer coating liquids H-3₀, H-3₃ and H-3₆ andphotoreceptors HP-3₀, HP-3₃ and HP-3₆ were prepared.

Comparative Example 4

[0198] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 98.0%, a rutile titanium oxide content of 40% and anaverage particle diameter of 0.02 μm.

[0199] Thus, undercoat layer coating liquids H-4₀, H-4₃ and H-4₆ andphotoreceptors HP-4₀, HP-4₃ and HP-4₆ were prepared.

Comparative Example 5

[0200] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.5%, a rutile titanium oxide content of 0% and anaverage particle diameter of 0.02 μm.

[0201] Thus, undercoat layer coating liquids H-5₀, H-5₃ and H-5₆ andphotoreceptors HP-5₀, HP-5₃ and HP-5₆ were prepared.

Comparative Example 6

[0202] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.5%, a rutile titanium oxide content of 0% and anaverage particle diameter of 0.35 μm.

[0203] Thus, undercoat layer coating liquids H-6₀, H-6₃ and H-6₆ andphotoreceptors HP-6₀, HP-6₃ and HP-6₆ were prepared.

Comparative Example 7

[0204] The procedures for preparation and evaluation of the undercoatlayer coating liquids U-1₀, U-1₃ and U-1₆ and photoreceptors P-1₀, P-1₃and P-1₆ in Example 1 were repeated except that the titanium oxide usedin the undercoat layer coating liquid was replaced with titanium oxidehaving a purity of 99.5%, a rutile titanium oxide content of 0% and anaverage particle diameter of 0.07 μm.

[0205] Thus, undercoat layer coating liquids H-7₀, H-7₃ and H-7₆ andphotoreceptors HP-7₀, HP-7₃ and HP-7₆ were prepared.

[0206] The results are shown in Tables 1 and 2. TABLE 1 Large particlesBlack spots (pieces) (pieces) Abnor- (H)* 0 3 6 0 3 6 mal (mm) monthmonth month month month month image Ex. 1 7 0 0 0 0 0 0 None (U-1₀)(U-1₃) (U-1₆) (P-1₀) (P-1₃) (P-1₆) None Ex. 2 10 0 0 0 0 2 4 (U-2₀)(U-2₃) (U-2₆) (P-2₀) (P-2₃) (P-2₆) None Ex. 3 5 0 1 2 2 3 10 (U-₃ ₀)(U-3₃) (U-3₆) (P-3₀) (P-3₃) (P-3₆) None Ex. 4 5 0 3 5 1 4 10 (U-4₀)(U-4₃) (U-4₆) (P-4₀) (P-4₃) (P-4₆) None Ex. 5 5 0 0 0 0 0 0 (U-5₀)(U-5₃) (U-5₆) (P-5₀) (P-5₃) (P-5₆) None Ex. 6 5 0 0 0 0 0 0 (U-6₀)(U-6₃) (U-6₆) (P-6₀) (P-6₃) (P-6₆) None Ex. 7 10 0 1 2 0 2 6 (U-7₀)(U-7₃) (U-7₆) (P-7₀) (P-7₃) (P-7₆) None Ex. 8 5 0 0 0 0 0 0 (U-8₀)(U-8₃) (U-8₆) (P-8₀) (P-8₃) (P-8₆) None Comp. 5 3 10 12 5 13 25 Ex. 1(H-1₀) (H-1₃) (H-1₆) (HP-1₀) (HP-1₃) (HP-1₆) Moiré Comp. 58 1 5 10 5 2032 Ex. 2 (H-2₀) (H-2₃) (H-2₆) (HP-2₀) (HP-2₃) (HP-2₆) None Comp. 70 1 58 5 20 30 Ex. 3 (H-3₀) (H-3₃) (H-3₆) (HP-3₀) (HP-3₃) (HP-3₆) None Comp.5 1 3 7 3 8 18 Ex. 4 (H-4₀) (H-4₃) (H-4₆) (HP-4₀) (HP-4₃) (HP-4₆) MoiréComp. 6 6 11 16 12 18 30 Ex. 5 (H-5₀) (H-5₃) (H-5₆) (HP-5₀) (HP-5₃)(HP-5₆) Moiré Comp. 68 10 20 30 15 30 50 Ex. 6 (H-6₀) (H-6₃) (H-6₆)(HP-6₀) (HP-6₃) (HP-6₆) None Comp. 10 5 10 15 10 15 25 Ex. 7 (H-7₀)(H-7₃) (H-7₆) (HP-7₀) (HP-7₃) (HP-7₆) None

[0207] (H)*: the height of the clear portion of the coating liquid.TABLE 2 At the beginning of the At the End of the running test runningtest VD (-V) VL (-V) VD (-V) VL (-V) Ex. 1 900 120 890 140 Ex. 2 905 110890 110 Ex. 3 890 110 860 135 Ex. 4 900 120 905 125 Ex. 5 900 130 900135 Ex. 6 900 120 890 150 Ex. 7 905 130 920 170 Ex. 8 905 125 900 135Comp. 900 140 920 190 Ex. 1 Comp. 900 150 930 200 Ex. 2 Comp. 910 160940 230 Ex. 3 Comp. 920 180 950 280 Ex. 4 Comp. 860 200 770 310 Ex. 5Comp. 830 180 730 250 Ex. 6 Comp. 850 170 775 240 Ex. 7

[0208] As can be understood from the above description, since theundercoat layer coating liquid includes titanium oxide, which isdispersed in a resin and an organic solvent and which has an averageparticle diameter greater than 0.05 μm and less than 0.20 μm and arutile titanium oxide content of from 10 to 100%, the resultant coatingliquid has preservation stability (i.e., good pigment dispersion) andthe resultant undercoat layer has good hiding power and good filmformability (i.e., pinholes are hardly formed in the resultant undercoatlayer). Therefore the resultant photoreceptor can produce high qualityimages with hardly causing abnormal images such as black spots, moiréand background fouling. When the titanium oxide has a rutile titaniumoxide content of from 10 to 100%, images with less background foulingcan be produced.

[0209] When the titanium oxide further has a purity not less than 99.0%,the resultant photoreceptor can maintain good electrophotographicproperties even when environmental conditions (e.g., humidity) changeand/or the photoreceptor is repeatedly used for a long period of time.In particular, occurrence of black spots can be avoided.

[0210] When the rutile titanium oxide content is from 30 to 70%,background fouling can be further improved.

[0211] This document claims priority and contains subject matter relatedto Japanese Patent Application No. 2001-282368, filed on Sep. 17, 2001incorporated herein by reference.

[0212] Having now fully described the invention, it will be apparent toone of ordinary skill in the art that many changes and modifications canbe made thereto without departing from the spirit and scope of theinvention as set forth therein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A coating liquid comprising: a binder resin;titanium oxide; and an organic solvent, wherein the titanium oxidecomprises rutile titanium oxide in an amount of from 10 to 100% byweight based on total weight of the titanium oxide, and wherein saidtitanium oxide is dispersed in the binder resin and organic solvent, andhas an average particle diameter greater than 0.05 μm and less than 0.20μm.
 2. The coating liquid according to claim 1, wherein the titaniumoxide has a purity of not less than 99.0% by weight.
 3. The coatingliquid according to claim 1, wherein the titanium oxide comprises 30 to70% by weight rutile titanium oxide based on the total weight of thetitanium oxide.
 4. A photoreceptor comprising: an electroconductivesubstrate; an undercoat layer located overlying the electroconductivesubstrate and comprising titanium oxide, said titanium oxide having anaverage particle diameter greater than 0.05 μm and less than 0.20 μm andcomprising rutile titanium oxide in an amount of from 10 to 100% byweight based on total weight of the titanium oxide; and a photosensitivelayer overlying the undercoat layer.
 5. The photoreceptor according toclaim 4, wherein the titanium oxide has a purity of not less than 99.0%by weight.
 6. The photoreceptor according to claim 4, wherein thetitanium oxide comprises 30 to 70% by weight rutile titanium oxide basedon the total weight of the titanium oxide.
 7. The photoreceptoraccording to claim 4, wherein the photosensitive layer comprises acharge generation layer and a charge transport layer.
 8. Anelectrophotographic image forming method comprising: charging aphotoreceptor; irradiating the photoreceptor with imagewise light toform an electrostatic latent image on the photoreceptor using a lightsource selected from the group consisting of laser diodes and lightemitting diodes; developing the electrostatic latent image with adeveloper including a toner to form a toner image on the photoreceptorusing a reverse development method; and transferring the toner imageonto a receiving material, wherein the photoreceptor comprises: anelectroconductive substrate; an undercoat layer located overlying theelectroconductive substrate and comprising titanium oxide, said titaniumoxide having an average particle diameter greater than 0.05 μm and lessthan 0.20 μm and comprising rutile titanium oxide in an amount of from10 to 100% by weight based on total weight of the titanium oxide; and aphotosensitive layer overlying the undercoat layer.
 9. Theelectrophotographic image forming method according to claim 8, whereinthe titanium oxide has a purity of not less than 99.0% by weight. 10.The electrophotographic image forming method according to claim 8,wherein the titanium oxide comprises 30 to 70% by weight rutile titaniumoxide based on the total weight of the titanium oxide.
 11. Theelectrophotographic image forming method according to claim 8, whereinthe photosensitive layer comprises a charge generation layer and acharge transport layer.
 12. An electrophotographic image formingapparatus comprising: a photoreceptor; a charger configured to chargethe photoreceptor; an image irradiator configured to irradiate thephotoreceptor with imagewise light to form an electrostatic latent imageon the photoreceptor; an image developer configured to develop theelectrostatic latent image with a developer including a toner to form atoner image on the photoreceptor; an image transfer device configured totransfer the toner image onto a receiving material; and a dischargerconfigured to reducing a charge remaining on the photoreceptor, whereinthe photoreceptor comprises: an electroconductive substrate; anundercoat layer located overlying the electroconductive substrate andcomprising titanium oxide, said titanium oxide having an averageparticle diameter greater than 0.05 μm and less than 0.20 μm andcomprising rutile titanium oxide in an amount of from 10 to 100% byweight based on total weight of the titanium oxide; and a photosensitivelayer overlying the undercoat layer.
 13. The electrophotographic imageforming apparatus according to claim 12, wherein the titanium oxide hasa purity of not less than 99.0% by weight.
 14. The electrophotographicimage forming apparatus according to claim 12, wherein the titaniumoxide comprises 30 to 70% by weight rutile titanium oxide based on thetotal weight of the titanium oxide.
 15. The electrophotographic imageforming apparatus according to claim 12, wherein the photosensitivelayer comprises a charge generation layer and a charge transport layer.16. A process cartridge comprising: a photoreceptor; and at least one ofa) a charger configured to charge the photoreceptor; b) an imageirradiator configured to irradiate the photoreceptor with imagewiselight to form an electrostatic latent image on the photoreceptor; c) animage developer configured to develop the electrostatic latent imagewith a developer including a toner to form a toner image on thephotoreceptor; d) an image transfer device configured to transfer thetoner image onto a receiving material; and e) a discharger configured toreducing a charge remaining on the photoreceptor, wherein thephotoreceptor comprises: an electroconductive substrate; an undercoatlayer located overlying the electroconductive substrate and comprisingtitanium oxide, said titanium oxide having an average particle diametergreater than 0.05 μm and less than 0.20 μm and comprising rutiletitanium oxide in an amount of from 10 to 100% by weight based on totalweight of the titanium oxide; and a photosensitive layer overlying theundercoat layer.
 17. The process cartridge according to claim 16,wherein the titanium oxide has a purity of not less than 99.0% byweight.
 18. The process cartridge according to claim 16, wherein thetitanium oxide comprises 30 to 70% by weight rutile titanium oxide basedon the total weight of the titanium oxide.
 19. The process cartridgeaccording to claim 16, wherein the photosensitive layer comprises acharge generation layer and a charge transport layer.
 20. A method formanufacturing a photoreceptor comprising: coating an undercoat layercoating liquid on an electroconductive substrate to form an undercoatlayer on the electroconductive substrate; and coating a photosensitivelayer coating liquid comprising a charge generation material and acharge transport material to form a photosensitive layer overlying theundercoat layer, wherein the undercoat layer coating liquid comprises: abinder resin; titanium oxide; and an organic solvent, wherein thetitanium oxide comprises rutile titanium oxide in an amount of from 10to 100% by weight based on total weight of the titanium oxide, andwherein said titanium oxide is dispersed in the binder resin and organicsolvent, and has an average particle diameter greater than 0.05 μm andless than 0.20 μm.
 21. The method according to claim 20, wherein thetitanium oxide has a purity of not less than 99.0% by weight.
 22. Themethod according to claim 20, wherein the titanium oxide comprises 30 to70% by weight rutile titanium oxide based on the total weight of thetitanium oxide.
 23. The method according to claim 20, wherein coating aphotosensitive layer coating liquid comprises: coating a chargegeneration layer coating liquid comprising the charge generationmaterial; and coating a charge transport layer coating liquid comprisingthe charge transport material.